The need for purification of liquids such as water, wastewater, processed foods, pharmaceuticals and industrial coolants is well known. In the past, most disinfection was by thermal or chemical means and in the case of water and wastewater, the principal disinfector has been chlorine. However, chlorine in most of its forms is highly reactive, poisonous and caustic. More recently, chlorine has been linked to cancer-producing agents in drinking water.
Thermal disinfection also is limited to material which can be heated to boiling temperatures or higher and maintained at those temperatures for prolonged periods. Some spore forming bacteria will survive temperatures of 123.degree. C for periods in excess of 30 minutes.
Some liquids cannot be treated with chemical disinfectants nor can they be subjected to prolonged boiling temperatures without destroying some essential characteristics. These include certain pharmaceuticals, some processed foods and many industrial coolants.
In purification, there is often a need to clarify or separate out various foreign matter. In wastewater treatment, special flocculants or coagulating agents such as alum are added to improve the separation of solid matter, the general practice being to treat the solids separately and in most cases, the solids are disposed of without disinfection.
In treatment of water and wastewater, Biochemical Oxygen Demand (BOD) or Oxygen Demand (OD) is a criteria of water purity. Chemical disinfection increases the BOD necessitating aeration to improve the dissolved oxygen content of the water and to oxidize the disinfectant. Then additives, such as calcium carbonate, are utilized to counteract the taste and odor of the disinfectant in drinking water. These additives need to be removed prior to use adding another step to the purification process.
Purification of liquids entails the use of energy in one form or another and the level of liquid purity is usually directly related to the energy input.
In the past, treatment of materials by microwave irradiation has been suggested; however, because of complexities; such as lack of homogenity, variations in electrical characteristics of each material and the energy containment and emission problem; practical microwave systems have not heretofore been developed.
Water, the most extensive and allotropic of all known solvents, may contain solids, gases and/or other liquids altering the dielectric constant, electrical conductivity and resultant microwave absorption. Therefore, a constant monitoring and control is necessary during treatment to assure purification and maximum energy efficiency.